Adsorption of antimony(III) on goethite in the presence of competitive anions

Abstract

Adsorption of antimony (Sb) on goethite affects its mobility and bioavailability in the environment. In natural systems, competitive anions may compete with Sb adsorption sites on goethite surface. Accordingly, the adsorption of Sb(III) on goethite was investigated in the presence of competitive anions. Kinetic studies suggest that adsorption reaction of Sb(III) on goethite is rapid initially and becoming slow after 8h both in binary Sb(III)–goethite system and in ternary Sb(III)-competitive anions–goethite system. Kinetic and adsorption isotherm studies show that PO43− significantly decreased the adsorption of Sb(III) on goethite, while both NO3− and SO42− had no effect. The adsorption data of Sb(III) on goethite in the absence and presence of competitive anions at three temperatures were successfully modeled using Langmuir (r2>0.932) and Freundlich (r2>0.975) isotherms. The thermodynamic parameters (∆G, ∆H, and ∆S) were calculated from the temperature dependence, suggesting that the adsorption process is spontaneous and exothermic. Accompanied by the adsorption of Sb(III) on goethite, significant oxidation of Sb(III) bound to the surface of goethite had occurred under the experimental conditions used in this study. Consequently, Sb(V) was released into the solution.